Abstract
In this work, we present for the first time a laser-based dual gas sensor utilizing a silica-based Antiresonant Hollow-Core Fiber (ARHCF) operating in the Near- and Mid-Infrared spectral region. A 1-m-long fiber with an 84-µm diameter air-core was implemented as a low-volume absorption cell in a sensor configuration utilizing the simple and well-known Wavelength Modulation Spectroscopy (WMS) method. The fiber was filled with a mixture of methane (CH4) and carbon dioxide (CO2), and a simultaneous detection of both gases was demonstrated targeting their transitions at 3.334 µm and 1.574 µm, respectively. Due to excellent guidance properties of the fiber and low background noise, the proposed sensor reached a detection limit down to 24 parts-per-billion by volume for CH4 and 144 parts-per-million by volume for CO2. The obtained results confirm the suitability of ARHCF for efficient use in gas sensing applications for over a broad spectral range. Thanks to the demonstrated low loss, such fibers with lengths of over one meter can be used for increasing the laser-gas molecules interaction path, substituting bulk optics-based multipass cells, while delivering required flexibility, compactness, reliability and enhancement in the sensor’s sensitivity.
Highlights
Hollow-core fiber (HCF) technology has experienced rapid and persistent development since the first photonic bandgap HCF was reported by Cregan et al in the previous century [1]
In order to eliminate ambient air from the air core of the Antiresonant Hollow-Core Fiber (ARHCF), the fiber was background signal due to the atmospheric concentration of the selected gas molecules), the fiber was firstly rapidly flushed with pure nitrogen (N2) at the pressure of 1200 Torr and subsequently filled firstlywith rapidly flushed with pure nitrogen (N2 ) at the pressure of 1200 Torr and subsequently filled with a calibrated mixture of the target gases at a slight and well-controlled pressure of 800 Torr
The performed experiments proved that the multi-band low-loss transmission of the ARHCFs can be conveniently used as an advantage, enabling simultaneous and efficient detection of dissimilar gases with their absorption features both in the Near- and Mid-Infrared spectral regions
Summary
Hollow-core fiber (HCF) technology has experienced rapid and persistent development since the first photonic bandgap HCF was reported by Cregan et al in the previous century [1]. Many types of HCFs have been designed and fabricated in order to obtain the lowest possible loss and single-mode guidance, while delivering desired versatility and reliability [2,3,4,5,6]. Despite being fabricated from high purity silica glass, such fibers (dependent on the type) enable low-loss light propagation in both. With proper design of the sensor, laser gas spectroscopy techniques can take advantage of the guidance performance of the HCFs and the air-core structure, which can be filled with any gas sample (single gas or a gas mixture). Low-volume fiber-based gas absorption cells providing optical path-lengths (gas molecules—laser light interaction path) precisely fitted to the specific application can be constructed
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